MTT assay

Vero cells were planted in 96-well plates (10⁴ cells per well) and cultured at 37 ℃ for 24 h. The cell culture medium was then replaced with fresh medium containing candidate peptides in a series of concentrations, and the plates were incubated at 37 ℃ for another 48 h. Afterwards, 20 μl of MTT solution (5 mg/mL in phosphate buffered saline, PBS) was added to each well, and the plates were incubated at 37 ℃ for 4 h. The medium was removed, and 100 μl of dimethyl sulfoxide (DMSO) was added to each well, and the plates were shaken gently for 10 min at room temperature to completely dissolve the crystal purple formazan. The absorbance was then measured at 570 nm using a microplate reader (BioTek, Winooski, VT, USA).